TRADITIONAL TREATMENT OPTIONS

Waste hypochlorite streams are generally produced when a chlorine laden gas is scrubbed using a recirculating caustic liquor.

Traditionally two methods have been used to destroy hypochlorite in effluent streams: metal slurry catalysis and the much more common chemical reduction. Compared with HYDECAT™, both tend to require close control (involving operator input) and comparatively complex dosing/control systems, valves and tanks.

Metal slurry catalysis utilises solutions of nickel, iron or cobalt added to the waste stream in stirred or agitated tanks, causing the same basic chemical destruction of the hypochlorite as in the HYDECAT process.

The high pH of the effluent causes precipitation of the metal as insoluble salt which is then removed and regenerated.

Alternatively, using a fine dispersion of an insoluble salt removes the need for the catalyst regeneration stage.

In either case the process is very dependent on temperature, pH and hypochlorite concentration, and must be carefully controlled to avoid runaway thermal reactions.

The reaction time combined with the settling of the catalyst slurry takes several days.

An important environmental drawback is that the final effluent is prone to contamination by heavy metal salts.